A throttle valve is arranged in an intake passage of an engine. When the ambient temperature falls to below the freezing point while the engine is stopped, the moisture in air condenses and freezes. As a result, the throttle valve becomes stuck in position where it was located when the engine stopped. Thus, patent document 1 discloses a technique that controls a throttle valve to open when the engine stops to ensure that intake air is obtained when the engine is started even if the throttle valve freezes.